Phenotypic and genetic aspects of host cell invasion by Salmonella species

Abstract

Salmonella species are enteric pathogens that successfully infect a host by crossing the epithelial cell barrier of the small bowel and subsequently invade the deeper tissue of the host. The events that occur at the epithelial surface of host cells during Salmonella entry have been the subject of considerable study in animal models and in cell culture. The development of in vitro tissue culture models, which successfully reproduce the interactions that occur between bacteria and host cells during invasion, has been invaluable in evaluating the contribution of bacterial and host cell factors in Salmonella entry. Tissue culture experiments have shown that only actively growing bacteria are capable of invading mammalian cells, while the host cell response is characterized by cytoskeletal changes that are accompanied by alterations in calcium ion flux and host cell protein phosphorylation. Bacterial growth in both low-oxygen and high-osmolarity conditions seem to induce the expression of proteins, which influence the ability of Salmonella to enter cells. Loci necessary for bacterial entry into mammalian cells have been identified using genetic techniques. It is not yet clear whether these genes encode structural or regulatory elements. Currently, work is underway to identify the host cell signal pathway affected by microbial invasion.